ACR MLG FLT CREW HEARD AND READ BACK A WRONG ALT. CTLR MISSED ERRONEOUS READBACK AND ALLOWED ACFT TO ENTER ADJACENT AIRSPACE WITHOUT COORD.

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MLG X WAS DSNDED TO 12000'. MLG X READ BACK 10000'. I DID NOT HEAR THE 10000' READ BACK. ONLY AFTER LISTENING TO THE TAPE RECORDING DID I KNOW THAT THE WRONG ALT WAS READ BACK. PRIOR TO THIS ALT; MLG X HAD READ BACK THE WRONG RWY ASSIGNMENT; WHICH I CAUGHT. I THEN TRANSFERRED THE FLT TO ANOTHER FREQ. AT THAT TIME; MLG X DSNDED BELOW 11000' AND AN ACFT (MLG Y) WAS CLBING OUT TO 10000'. DEP CTL ISSUED THE TFC. BOTH ACFT WERE ISSUED TURNS AWAY FROM EACH OTHER. AT THIS TIME; A DATA REDUCTION HAS NOT BEEN ACCOMPLISHED AND I DO NOT KNOW IF A LOSS OF STANDARD SEP OCCURRED. MLG Y WAS ALSO TOLD TO MAINTAIN VISUAL SEP FROM MLG X. AT WHAT POINT THIS OCCURRED; I DO NOT KNOW. MLG X CONTINUED AND LANDED W/O INCIDENT. CALLBACK CONVERSATION WITH RPTR REVEALED FOLLOWING INFO. DURING THE FAC'S INVESTIGATION OF THIS INCIDENT; IT WAS FOUND THAT AT THE TIME THAT ALT SEP WAS LOST; LATERAL SEP EXISTED IN THE FORM OF COURSE DIVERGENCE. RPTR WAS CHARGED WITH A SYS DEVIATION FOR ENTERING DEP CTL'S AIRSPACE W/O AUTH.